1. Field of the Invention
This invention relates to a method and apparatus for repairing defects in photomasks used in the manufacture of semiconductor microcircuits and other electronic components to transfer a pattern onto a workpiece and, in particular, to repairing clear (transparent) defects in attenuated phase shift masks. The defects are in the form of pin holes or entire missing portions in the mask pattern which defects are transferred eventually to the electronic component substrate during use of the attenuated mask.
2. Description of Related Art
In the manufacture of circuit patterns on electronic components such as the manufacture of integrated circuits on semiconductor substrates photomasks are used to transfer the desired circuit pattern onto the substrate workpiece. Typically, a photomask comprises a patterned film such as chromium, nickel, aluminum or molysilicide deposited on a transparent base such as glass or quartz. The photomask is generally manufactured by depositing a thin layer of the film on the surface of the transparent substrate, coating the film with a photoresist coating, exposing the desired pattern on the photoresist coating, developing the resist coating, and removing the film from the unprotected areas by etching leaving a patterned film on the substrate.
The pattern contained in the photomask is reproduced onto the surface of a workpiece typically by placing the mask over the workpiece and irradiating a radiation-sensitive resist material on the workpiece. The variety of radiation sources for lithography that have been used or proposed include visible light, ultraviolet light, x-ray radiation, electrons and ions. When illuminated by the radiation, the pattern on the photomask serves to selectively block portions of the radiation beam while allowing other portions to be transmitted therethrough. In this manner, complex geometries having very narrow line widths can be reproduced allowing the economical production of very large scale integrated circuits and other devices.
A photomask is typically employed a large number of times for the production of numerous electronic devices. This places stringent demands on the quality of a photomask since any flaws or defects in the photomask are reproduced in the workpiece which directly effects the operability of the workpiece.
The process of fabricating photomasks, however, typically causes several defects in the pattern. The defects are usually classified as opaque and clear with opaque defects arising where excess film material exists in an unwanted area and clear defects arising where the film material is missing from a desired area such as a pinhole in a line pattern.
Method and apparatus are commercially available for repairing mask defects by focusing an ion beam on the defect area. A gas such as organometallic gas WF6, trimethylaluminum, or the like is discharged from a gas nozzle and the gas is supplied in the vicinity of the defect. The defect portion is irradiated by the ion beam simultaneously. By doing so, the gas is decomposed by irradiation of the ion beam and a metal, carbon and the like which is the component of the gas selectively forms a thin film on the defect portion. In this manner, the defect portion is repaired. Basically, a patch is provided in the clear defect which patch forms an opaque portion repairing the clear defect. Such apparatus use backscattering electrons for imaging and are automated including computer control of an optical X-Y table and the ion beam source so that a mask can be scanned, the position of clear defects is noted from other inspection systems and the data placed in the apparatus for computer controlled positioning of the mask and operation of the ion beam to patch the clear defects.
A number of patents have issued in the art of repairing defective photomasks and include U.S. Pat. Nos. 4,952,421; 5,104,684; 5,506,080, 5,799,104; and 5,882,823. These patents discuss the various type photomasks and the different methods employed to repair defects on the mask and the disclosures of each of the above patents are hereby incorporated by reference. The following description will be directed to the repair of attenuated masks such as masks containing a layer of MoSi on a quartz substrate but it will be appreciated by those skilled in the art that the invention applies to other masks such as optical masks, x-ray masks, attenuated phase shift masks and alternating phase shift masks which may be made using a variety of metals as the patterning design such as chrome, MoSi, and chrome oxide fluoride on a variety of substrates.
The type of mask to which this invention is particularly directed is an attenuated mask which is generally built using a transfer layer of chrome that allows the chrome to act as a mask to the attenuated film under the chrome layer. The transfer layer of chrome is generally patterned as noted above with the differences being that the chrome will eventually be removed exposing a pattern of attenuated material under the chrome forming the desired attenuated mask circuit pattern.
Bearing in mind the problems and deficiencies of the prior art, it is an object of the present invention to provide a method to repair clear defects in photomasks used to make electronic components such as semiconductors.
It is a further object of the invention to provide an apparatus to repair clear defects in photomasks used to make semiconductor electronic components.
It is another object of the invention to provide photomasks made in accordance with the method and apparatus of the invention.
It is another object of the present invention to provide a method to repair transparent defects in attenuated masks which are used to make electronic components such as semiconductors.
It is a further object of the present invention to provide an apparatus to repair transparent defects in attenuated photomasks used to make semiconductors and other electronic components.
A further object of the invention is to provide attenuated photomasks made in accordance with the method and apparatus of the invention.
Other advantages of the invention will be readily apparent from the following description.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed, in a first aspect, to a method of repairing a mask defect in a pattern layer on a substrate wherein the defect has sidewalls in the pattern layer the layer having a top surface and a bottom surface and being positioned on a top surface of a substrate comprising the steps of:
undercutting the sidewalls of the defect to form new sidewalls having an angle wherein the top surface of the pattern layer overhangs the lower surface of the pattern layer; and
filling the undercut defect with a repair material.
In a further aspect of the invention, a method is provided for repairing a photolithography mask defect in a pattern layer on a substrate wherein the defect has sidewalls in the pattern layer the layer having a top surface and a bottom surface and being positioned on a top surface of a substrate comprising the steps of:
undercutting the sidewalls of the defect to form new sidewalls having an angle, wherein the top surface of the pattern layer overhangs the lower surface of the pattern layer;
depositing a first portion of a first repair material on the new sidewall and preferably depositing the first repair material to maintain the same new sidewall angle; and
depositing a second portion of a second repair material preferably substantially perpendicular to the top surface of the pattern layer, the second portion contacting the first portion and filling the defect.
In another aspect of the invention, an apparatus is provided for repairing clear defects in photomasks used in the manufacture of electronic components such as semiconductors, the photomask having a defect in a circuit pattern layer thereon wherein the defect has sidewalls in the pattern layer the layer having a top surface and a bottom surface and being positioned on a substrate comprising:
a holding device for securing a photomask comprising a substrate and a circuit pattern layer thereon;
moving means for moving the secured photomask in an X-Y plane;
detecting means for locating and identifying a clear defect in the pattern layer, which defect has sidewalls in the pattern layer;
energy means to direct an angled energy beam at the surface of the photomask for removing pattern layer material from the sidewall of the photomask;
positioning means to position the photomask under the energy means so that the energy beam will be directed to a particular X-Y position of the photomask whereby when the defect is to be repaired, the photomask is positioned and the energy means activated to ablate (undercut) the defect sidewalls of the photomask pattern to undercut the sidewalls to form new angled sidewalls so that the top surface of the pattern layer overhangs the lower surface of the pattern layer; and
filling means to fill the undercut defect with a repair material.
In a further aspect of the invention, the filling means is used to deposit a first repair material on the new sidewalls preferably maintaining the same sidewall angle and a second filling means is used to deposit a second repair material preferably substantially perpendicular to the top surface of the pattern layer, the second repair material contacting the first repair material and filling the defect.
Photomasks made by the method and using the apparatus of the invention are also provided herein.